Parasites in the thoracic ganglion of

We examined 149 marbled shore crabs, Pachygrapsus marmoratus, from the coast of Portugal for parasites. In particular, we focused our effort on the crab thoracic ganglion. The thoracic ganglion is the largest concentration of nervous tissue in a crab and thus, parasites associated with this organ are well situated to influence host behavior. We found metacercariae of two microphallid trematode species in the thoracic ganglion. We also found a microsporan and an apicomplexan associated with the thoracic ganglion. Other parasites not associated with the thoracic ganglion included gregarine trophozoites which were present in the digestive diverticulae in some of the crabs and the entoniscid isopod, Grapsion cavolini.Metacercariae of one of the trematodes (probably Microphallus pachygrapsi (Deblock and Prevot)), may influence the mortality of its host

Parasites in the thoracic ganglion of Pachygrapsus marmoratus (Brachyura: Grapsidae) from the coast of Portugal

We examined 149 marbled shore crabs, Pachygrapsus marmoratus, from the coast of Portugal for parasites. In particular, we focused our effort on the crab thoracic ganglion. The thoracic ganglion is the largest concentration of nervous tissue in a crab and thus, parasites associated with this organ are well situated to influence host behavior. We found metacercariae of two microphallid trematode species in the thoracic ganglion. We also found a microsporan and an apicomplexan associated with the thoracic ganglion. Other parasites not associated with the thoracic ganglion included gregarine trophozoites which were present in the digestive diverticulae in some of the crabs and the entoniscid isopod, Grapsion cavolini.Metacercariae of one of the trematodes (probably Microphallus pachygrapsi (Deblock and Prevot)), may influence the mortality of its host

Interactions between juvenile marine fish and gnathiid isopods: predation versus micropredation

Theory suggests that micropredators can be virulent and that they will impact smaller hosts more than larger ones. We examined the interactions between micropredatory gnathiid isopods and juvenile damselfish Acanthochromis polyacanthus, the only fish on the Great Barrier Reef without a pelagic larval stage. Compared to most other fishes, A. polyacanthus can potentially interact with reef-based micropredators much earlier in life. To determine whether gnathiid isopods feed on juvenile A. polyacanthus, 150 juvenile fish sub-sampled from 20 fish broods were surveyed for ectoparasites and micropredators. Gnathiids were associated with 5 A. polyacanthus broods with mean standard lengths (SL) between 4.2 and 21.1 mm. Gnathiids were also found attached to 5 individual A. polyacanthus juvenile

Diversity increases biomass production for trematode parasites in snails

Increasing species diversity typically increases biomass in experimental assemblages. But there is uncertainty concerning the mechanisms of diversity effects and whether experimental findings are relevant to ecological process in nature. Hosts for parasites provide natural, discrete replicates of parasite assemblages. We considered how diversity affects standing-stock biomass for a highly interactive parasite guild: trematode parasitic castrators in snails. In 185 naturally occurring habitat replicates (individual hosts), diverse parasite assemblages had greater biomass than single-species assemblages, including those of their most productive species. Additionally, positive diversity effects strengthened as species segregated along a secondary niche axis (space). The most subordinate species—also the most productive when alone—altered the general positive effect, and was associated with negative diversity effects on biomass. These findings, on a previously unstudied consumer class, extend previous research to illustrate that functional diversity and species identity may generally both explain how diversity influences biomass production in natural assemblages of competing species

Parasites of coral reef fish larvae: its role in the pelagic larval stage

The pelagic larval stage is a critical component of the life cycle of most coral reef fishes, but the adaptive significance of this stage remains controversial. One hypothesis is that migrating through the pelagic environment reduces the risk a larval fish has of being parasitised. Most organisms interact with parasites, often with significant, detrimental consequences for the hosts. However, little is known about the parasites that larval fish have upon settlement, and the factors that affect the levels of parasitism. At settlement, coral reef fishes vary greatly in size and age (pelagic larval duration), which may influence the degree of parasitism. We identified and quantified the parasites of pre-settlement larvae from 44 species of coral reef fishes from the Great Barrier Reef and explored their relationship with host size and age at settlement, and phylogeny. Overall, less than 50% of the larval fishes were infected with parasites, and over 99% of these were endoparasites. A Bayesian phylogenetic regression was used to analyse host-parasite (presence and intensity) associations. The analysis showed parasite presence was not significantly related to fish size, and parasite intensity was not significantly related to fish age. A phylogenetic signal was detected for both parasite presence and intensity, indicating that, overall, closely related fish species were likely to have more similar susceptibility to parasites and similar levels of parasitism when compared to more distantly related species. The low prevalence of infection with any parasite type and the striking rarity of ectoparasites is consistent with the 'parasite avoidance hypothesis', which proposes that the pelagic phase of coral reef fishes results in reduced levels of parasitism

Parasites in food webs: the ultimate missing links

Parasitism is the most common consumer strategy among organisms, yet only recently has there been a call for the inclusion of infectious disease agents in food webs. The value of this effort hinges on whether parasites affect food-web properties. Increasing evidence suggests that parasites have the potential to uniquely alter food-web topology in terms of chain length, connectance and robustness. In addition, parasites might affect food-web stability, interaction strength and energy flow. Food-web structure also affects infectious disease dynamics because parasites depend on the ecological networks in which they live. Empirically, incorporating parasites into food webs is straightforward. We may start with existing food webs and add parasites as nodes, or we may try to build food webs around systems for which we already have a good understanding of infectious processes. In the future, perhaps researchers will add parasites while they construct food webs. Less clear is how food-web theory can accommodate parasites. This is a deep and central problem in theoretical biology and applied mathematics. For instance, is representing parasites with complex life cycles as a single node equivalent to representing other species with ontogenetic niche shifts as a single node? Can parasitism fit into fundamental frameworks such as the niche model? Can we integrate infectious disease models into the emerging field of dynamic food-web modelling? Future progress will benefit from interdisciplinary collaborations between ecologists and infectious disease biologists